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Technical Manual
An on onboard EEPROM stores all of the user channel related data such as
frequencies, CTCSS tones etc. A serial port at the Microphone accessory socket of the
MX920 provides access to the Controller card software configurations for the purpose
of the user to create and change this channel related information.
Special functions capable of being carried out include non-predictive full duplex
CTCSS encoding/decoding, DCS encoding/decoding as well as 5-Tone and DTMF
signalling. Digipots under the control of the processor ensure that user set up levels
for TX deviation and power levels are correctly set for each channel.
1.2.2 Power Amplifier Module
The PA receives the low level modulated RF signal from the Exciter RF output and
amplifies and filters it to final output power level. Forward and reflected power
voltages are fed to the Micro Controller.
The PA is very compact and efficient for high reliability and low cost. The heatsink
has minimal temperature rise even under continuous operation, ensuring the best
MTBF obtainable for a practical design. A low loss 13 element elliptical low pass
filter ensures that harmonics remain below –90 dBc. The new PA module uses the
latest LDMOS technology and using only two active RF transistors improves
efficiency and increases the operating bandwidth. At the same time this reduces the
number of components used and further improves the long term reliability.
© SPECTRA ENGINEERING 2003 Revision 1.1.4
Installation and Operation
7
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